In general, the use of inflatable crash bags for protecting drivers and passengers involved in vehicular accidents is widely known.
In early versions of such devices, a compressed gas such as air, carbon dioxide, or nitrogen was stored, in situ, in a pressure bottle or flask, the valving of which was activated by sensing means responsive to rapid change in velocity or direct impact.
Generally speaking, such devices were found unsatisfactory because of slow crash bag-inflation rates plus the difficulty of maintaining a pressure bottle or flask at the required pressure level over an indefinite period of time.
As a result, stored gas systems have now been generally replaced by gas-generating propellant compositions, particularly exothermic gas-generating propellants.
In general the most frequently used crash bag propellants contain an azide salt capable of reacting with an oxidizer to produce nitrogen gas. Typical are the following idealized reactions: EQU 2NaN.sub.3 +CuO.fwdarw.3N.sub.2 +Cu+Na.sub.2 O [1] EQU 6NaN.sub.3 +Fe.sub.2 O.sub.3 .fwdarw.9N.sub.2 +2Fe+3Na.sub.2 O [2]
in which elemental metal such as copper or iron and sodium oxide (Na.sub.2 O) are obtained as by-products.
While copper and iron have little toxicity in their elemental forms, Na.sub.2 O and similar alkali and alkaline earth metal oxides remain potentially corrosive and/or toxic, owing to their caustic effect on tissue. Nitrogen gas obtained by reacting metal azides and oxidizers, as above described, frequently contains substantial amounts of alkali metal oxides and corresponding hydroxides within the product gas in the form of dust and aerosols. In addition, azides are capable of reacting with available acids and certain metals to form undesired shock-sensitive intermediate compounds.
In general, an ideal propellant system for crash bags must (a) have a relatively fast reaction time (10-60 milliseconds), (b) the generated gas and other reaction by products must be essentially non-toxic and non-corrosive in nature, (c) the underlying exothermic reaction must not generate excessive heat capable of burning a user or weakening the crash bag itself, (d) the propellant composition must retain its stability and reactivity for relatively long periods of time under at least normal driving conditions, and (e) the amount of propellant, its packaging, and the crash bag itself must be compact and easily storable within a steering column and/or dashboard.
Basic to the above listed criteria, however, is the ability to safely produce a propellant composition capable of producing a positive oxygen balance to avoid excessive production of poisonous carbon monoxide, and a structurally stable volume/surface area grain configuration which is workable for an extended period of time under a wide range of temperature and other conditions.
In particular, in order to achieve good control over burning rates and also to prevent segregation of reactants, propellants must be produced and used in a consolidated or aggregated form. Conventionally this requires a tabletting procedure since conventional extrusion and granulation procedures require polymeric binders which produce an excessive amount of carbon monoxide and other toxic by products.
Efforts to meet the above criteria are conventionally reflected, for instance, in the use of alkali metal azides combined with an alkali metal oxidant plus an amide or tetrazole (U.S. Pat. No. 3,912,561); silicon dioxide with an alkali or alkaline earth metal azide plus a nitrite or perchlorate (U.S. Pat. No. 4,021,275); an alkali metal azide with a metal halide (U.S. Pat. No. 4,157,648); a plurality of metal azides with metal sulfides, metal oxides and sulfur (U.S. Pat. No. 3,741,585); an alkali or alkaline earth metal azide with a peroxide, perchlorate or nitrate (U.S. Pat. No. 3,883,373); an alkali metal azide with a metal oxide (iron, titanium or copper) (U.S. Pat. No. 3,895,098); an alkali metal-or alkaline earth metal-azide with an oxidant consisting of iron oxide combined with up to 1 wt. % of nickel or cobalt oxide (U.S. Pat. No. 4,376,002); and an alkali-or alkaline earth metal-azide combined with an oxidant obtained by forming a hydrated gel of a suitable base and metal salt, which is thereafter dehydrated in the presence of a metal oxide of aluminum, magnesium, chromium, manganese, iron, cobalt, copper, nickel, cerium and various transition series elements (U.S. Pat. No. 4,533,416).
Because of the above-enumerated difficulties with the basic azide reaction there appears to be a substantial advantage in avoiding its use altogether, provided the remaining problems can still be solved.
Attempts in this direction, however, have generally failed because of negative oxygen balances with the formation of unacceptable amounts of carbon monoxide. Conventional "smokeless"-type propellants of a single base type, in particular, have been found unsatisfactory because of the need for an extrusion and granulation step and the above-noted tendency to generate excess carbon monoxide using conventional binders associated with known propellant extrusion techniques.
Use of triazole and tetrazole reactants (U.S. Pat. Nos. 4,948,439 and 4,931,112) and metal nitrides (U.S. Pat. No. 4,865,667) have also been attempted, however, none of the resulting modified propellant grains appear to be sufficiently stable to meet the above criteria.
It is an object of the present invention to safely and efficiently obtain a structurally and chemically stable non-azide type propellant composition capable of rapidly and consistently producing high quality nitrogen gas suitable for crash bag systems, inclusive of a practical extrusion process for low temperature production of smokeless-type propellant composition(s).